1. Field of the Invention
The present invention relates to a capacitive writing device, and more particularly, to a cordless capacitive writing device in phase with a touch sensor.
2. Description of the Prior Art
A conventional mutual capacitive sensor is shown includes an insulating surface layer, a first conductive layer, a dielectric layer, a second conductive layer. The first conductive layer and the second conductive layer have a plurality of first conductive strips and a plurality of second conductive strips, respectively. Each of these conductive strips can be made up by a plurality of conductive pads and connecting lines 19 connected to the conductive pads in series.
In the process of mutual capacitive detection, one of the first conductive layer and the second conductive layer is driven, while the other of the first conductive layer and the second conductive layer is detected. For example, a driving signal is sequentially provided to each first conductive strip, and corresponding to each first conductive strip provided with the driving signal, signals from all of the second conductive strips are detected, which represent capacitive coupling signals at the intersections between the first conductive strip provided with the driving signal and all the second conductive strips. As a result, capacitive coupling signals at the intersections between all the first and second conductive strips are obtained to form an image of capacitive values.
The image of capacitive values at the time when there is no external touches is obtained as a reference. By comparing the difference between the reference image and the image of capacitive values later detected, the touch or approach of an external conductive object can be determined, and furthermore, the position touched or approached by the external conductive object can be determined.
However, the magnitude of this difference between the reference image and the image of capacitive values later detected is proportional to the area on the touch sensor approached or touched by an external conductive object, thus the area must be sufficiently large in order to be identified. Such a limitation therefore dictates the size of the pen head of a passive capacitive pen to be relatively large, preferably larger than 4 mm. The large pen head may block the view of a user from seeing the tip of the pen during writing. As a result, writing may not be accurately made at desired locations.
From the above it is clear that prior art still has shortcomings. In order to solve these problems, efforts have long been made in vain, while ordinary products and methods offering no appropriate structures and methods. Thus, there is a need in the industry for a novel technique that solves these problems.